BACKGROUND Mesenchymal stem cells (MSCs) with immunoregulatory properties affect immune systems. Many studies showed that antioxidants such as vitamin E (Vit E) and selenium (Se) could improve stem cells survival. This study aims to investigate the effects of MSC conditioned media (CM) treated with Vit E and Se on immune cells. METHODS MSCs were isolated and cultured with Vit E and Se. Immature dendritic cells (DCs) and peripheral blood mononuclear cells (PBMCs) were cultured with MSC CM treated with Vit E and Se. The expression of HLA-DR, CD86, CD40, and CD83 on mature DC were evaluated. DC supernatant and PBMCs supernatant was collected for the study of TGF-β, IL-10, and IL-12. PBMCs evaluated for the expression of T-bet, GATA3, RORγt, and FOXP3. RESULTS MSC CM increased CD40 on myeloid DC (mDC). CD40 has been decreased in DC treated with MSC (Vit E) and MSC (Se) CM. HLA-DR expression on DCs and IL-12 level were significantly reduced in MSC (Vit E) CM. IL-10 concentration increased in DCs treated with MSC (Vit E) and MSC (Se) CM. Treatment of PBMCs with MSC CM decreased IL-10 level, FOXP3, and RORγt expression. On the other hand, the MSC (Vit E) CM and MSC (Se) CM decreased the IL-10 level and increased IL-12, T-bet, and RORγt. CONCLUSIONS According to the results, the treatment of MSC with Vit E and Se enhanced the ability of MSCs to inhibit DCs and improved immunomodulatory effects. Concerning the effect of MSC on PBMC, it seems that it increased RORγt expression through monocytes.